Combustion control



Nv. l0, 1936. H, KEELEY 2,060,323

COMBUSTION CONTROL Filed Jan. 2, 1934 3 Sheets-Sheet 1 Nov. 10, 1936. H, J, KEELEY v 2,060,323

COMBUSTION CONTROL Filed Jan. 2, 1954 5 sneets-sheeft 2 NOV. 10, H; J KEELEY I l 2,060,323

COMBUSTION CONTROL Filed Jan. 2, 1954 y 3 Sh,=,e'f,s-SheecI 5 s r I mwnto/o l l Hf/v/Qy d Kite-Ey Patented Nov. 10, 1936 UNITED STATES PATENT OFFICE Application January 2,

14 Claims.

This invention relates to an electrical control system for fuel burners, and while it is more particularly designed for use with the burner' disclosed in applicants copending applications, Serial No. 691,649,1iled Sept. 30, 1933, and Serial No. 697,637, filed Nov. l1, 1933, it is of course not limited to use in connection with these particular installations.

The principal object of this invention is to provide a control system for fuel burner which will not only provide any desired preset temperature to the medium being heated, but will maintain this temperature with the greatest possible efciency of fuel consumption.

Another object of the invention is to provide a simple highly efficient electrical system which will control the amount of fuel being fed to a burner automatically in accordance with a relation between the temperature of the burner and the temperature of the cold outside air or other me- 20 dium which it is desired to heat.

A further object is to provide a. control circuit which will automatically control the amount of air being fed to a burner to obtain the most eiii- F cient relation between fiue gas temperature and the carbon dioxide content of the iiue gases, and so as to obtain a neutral flame at all times.

A still further object is to provide means for shutting down the entire plant should the re n fail to ignite or should the. iiame die out. o Thermostats have been heretofore applied to control the fuel feed of a heating plant burner in accordance with inside or room temperature without regard to outside temperatures. The present invention, however controls the fuel feed according to a relation between the. burner and the outside temperatures, thus should the outside temperature fall the re will be automatically increased without requiring a consequent lowering in the inside temperatures and vice versa.

The present invention also controls the air to the burner in accordance with the chemical requirements of the burning fuel and not in accordance with the amount thereof as in present installations. The control of air to a burner in consequence of flue gas temperature alone is not completely eiiicient operation since it does not take into consideration the carbon dioxide percentage in the fuel gases. The present invention controls the air automatically according to the requisite scientific relation between the. flue gas temperature and the carbon dioxide percentage to obtain complete combustion WthQllI EX- cess air at all times.

1934, Serial N0. 705,035

Other objects and advantages reside in the detail construction of the invention, which is designed for simplicity, economy, and efliciency. These will become more apparent from the following description.

In the following detailed description of the invention reference is had to the accompanying drawings which form a part hereof. Like numerals refer to like parts in all views of the drawings and throughout the description.

In the drawings:

Fig. 1 is a plan View of a portion of the control mechanism of a typical burner to vwhich the present control system is applicable.

Fig. 2 is a circuit diagram of the portion of the control system controlling the fuel feed to the burner.

Fig. 3 is a circuit diagram illustrating the control system for the air feed to the burner.

Fig. 4 is a circuit diagram illustrating a circuit for controlling the main current supply in accordance with a relation between the outside temperature and the steam pressure.

The burner feed mechanism of Fig. 1 is described and illustrated more in detail in applicants copending application, Serial No. 691,649, filed Sept. 30, 1933, and will but be briefly outlined here, to illustrate a typical feed mechanism to which the present invention may be applied. Briefly, it consists of a driving motor II) operating a cam II through the medium of a suitable reduction gear I2. The cam II reciprocates a ratchet member I3 which in turn drives a fuel feed conveyor I 4 through the medium of a ratchet gear I5 through suitable transmission gears I6. The ratchet member I3 can be made to engage more or less teeth of the ratchet gear I5 by movement of a wedge member II. The wedge member is moved into greater or less engagement by means of a fuel feed control motor I8.

The air for the burner is furnished from a blower I9, the intake of which, is controlled by a means of an arcuate rack 20 operated from an air control motor 2 I. The rack 20 and the wedge member II are simply illustrative of one of mechanical expedients for controlling the air and fuel supply. The motors 2| and I8 could be connected with any other desired mechanism which would control the air and fuel supply. The controls are preferably operated from low voltage direct current furnished by a D. C. generator 22 driven by the motor Ill, which in the usual installation would be an A. C. Motor.

In controlling the motor I8 a compact thermoresponsive device 23 is employed, as indicated diagrammatically in Fig. 2. This device con- 55 sists of two electrically controlled temperature gauge mechanisms, one of which actuates a hand 24 which may be the indicating hand of any standard electrically operated temperature gauge. The other mechanism similarly and independently controls an independent hand 25. The gauge mechanism for operating the hand 24 is connected through a pair of conductors 26 with a suitable thermo-couple positioned on the exterior of the building in which the heating plant is located so as to cause the hand 24 to move in consequence of the changes in exterior temperature. The mechanism for operating the hand 25 is connected by means of a pair of conductors 21 with a thermo-couple positioned in the rebox or bowl of the heater. The interior construction of the gauge 23 forms no part of the present invention, and may be any of the commercial thermogauges, the indicating hands of which could be used for the hands 24 and 25. For convenience, it will be assumed that the exterior temperature hand 24 moves to the right, Fig. 2, to indicate falling temperature and that the burner temperature hand 25 moves to the left to indicate a falling temperature.

The hands 24 and 25 are each provided with an electrical contact 28 and 29, respectively, Which are connected through conductors 30 with a polarized relay 3I. The polarized relay 3| consists of a rst electro-magnet 32 and a second electro-magnet 33 which alternately act upon an armature 34 to alternately close a contact 35 and a contact 36. The contacts 35 and 36 control the direction of rotation of the armature of the fuel feed control motor I8 which is connected by means of suitable conductors 31 with the generator 22. The electro-magnet 33 is always in circuit, through a resistance 38, with the generator 22 so that it will always be pulling the armature 34 toward the Contact 36. The electro-magnet 32 is in circuit with the thermo-gauge contacts 28 and 29 through a relatively smaller resistance 39.

Let us assume that the outside temperature is comparatively low so that the hand 24 is toward the right or low temperature position of Fig. 2 and that the re has been started in the burner. The operation of the generator 22 will energize the magnet 33 so as to close the contact 36 and cause the motor I8 to operate the wedge member I1, forwardly to increasingly feed fuel to the burner. Now let us assume that the fire raises the re box temperature to cause the hand 25 to swing toward the right. Eventually a position will be reached when the contacts 28 and 29 will close, thus closing the circuit to the magnet 32. The latter magnet will have a greater pull than the magnet 33, owing to the differences in the resistance 38 and 3S, soas to cause the armature 34 to close the contact 35. This reverses the motor I8 and causes it to gradually withdraw the Wedge member I1 and thus gradually reduce the amount of fuel by a feed to the burner. This will continue until the fire temperature begins again to fall so as to separate the hand 25 from the hand 24 and allow the fuel feed motor I8 to resume its forward direction.

Of course, as the combustion increases, the supply of air must also be increased. This is accomplished by the circuits shown in Fig. 3 in which a thermo-gauge 49 having a thermometer hand 4I is employed. The thermo-gauge 40 is connected through suitable conductors 42 with a thermo couple in the stack outlet of the heater and as the stack temperature rises, the hand 4I will swing to the right and as it lowers it will swing to the left. A pivoted rack lever 44, operated from a rack 45 and a worm 46, is incorporated in the thermo-gauge 40. The rack lever is provided with a contact 43 and the hand 4I is provided with a coacting contact 54. The worm 46 is driven from a small motor 41, the control of which will be later described.

The thermo-gauge 40 is for controlling the operation of the air feed motor 2| which is connected through suitable conductors 48 with the generator 22. The control is effected through a second polarized relay 49 similar to the previously described relay 3| and consisting of a first and second electromagnet 56 and 5I, respectively, and an armature 52 swinging between motor reversing contacts 53. Normally the armature is drawn toward the magnet 5I to cause the motor 2I to rotate, forwardly, in a direction which will gradually open the air intake of the blower I9. When the ilue gas temperature reaches a predetermined optimum point the contact 54 on the thermoresponsive hand 4I will close the contact 43, thereby energizing the magnet 55) and causing the armature 52 to reverse the direction of the motor 2I so as to gradually close the air intake to the blower I9.

The optimum point for reversing the motor 2| is a variable which cannot be efficiently preset in advance. The flue gas temperature may be affected by many things, such as the use of preheaters which would have a cooling effect on the flue gases and would lower the optimum point in the gauge 4I); unevenness in the fuel bed, blow holes, etc., would also effect the flue gas temperature by the passage of heat due to excess oxygen; variations in the fuel etc., would also affect it. All of these things would cause a movement in the hand 4I yet would not necessarily indicate the condition of combustion. Therefore, means are provided for moving the contact 43 in consequence of the actual CO2 percentage in the flue gases so as to always place the optimum point at the proper point for perfect combustion of the fuel then burning. This is accomplished through the medium of a CO2 indicator 55, having a hand 56 which moves in consequence of variations in the CO2 percentage in the stack gases. This may be any of the standard types of CO2 indicators which operate chemically or electrically. The indicator is connected with the stack filter elements or electrodes by means of suitable conductors 12. The indicator 55 controls the direction of rotation of a small motor 41 and through it the movement of the rack lever 44 so as to set the contact 43 at various points depending upon the CO2 content of the ue gases.

The small motor 41 is directly controlled from a relay 1I which in turn is controlled through conductors 13 from a pair of contacts 14 on an oil plunger relay 10. The relay 1I has left and right electromagnets 15 and 16, respectively, actuating an armature 11. The left electromagnet 15 is constantly energized through a suitable resistance and normally holds the armature 11 to the left, a position which causes the motor 41 to rotate forwardly and move the rack arm 44 to the right, away from the hand 4I. Action of the relay 10 to close the contacts 14 will swing the armature 11 and reverse the motor 41 to cause the rack arm to swing to the left.

The oil plunger relay 1D is operated from a pair of contacts 62 mounted on a rack arm 58 in the CO2 indicator. These contacts are closed by the contact closer 51 on the CO2 hand 56. They are connected by means of a pair of conductors to an electromagnet 68 in a relay 69. The relay 69 has a second electromagnet 18 which is constantly energized to pull an armature 19 against a contact 88. The armature 19 and contact 88 normally close the circuit to the oil plunger relay 18.

The rack arm 58 of the CO2 indicator is actuated by a motor 68 through a rack 59 and worm 6|. The motor 68 is controlled by differential, polarized, reversing relay 61, a magnet 8| of which is connected with olscale co-ntacts 64, of the indicator 55, through conductors 82. The contacts 64 are closed by a circuit closer 63 when the rack arm swings to its extreme right position. The relay 61 is of a type to hold the relay armature 83 against the last energized magnet when the energizing current is 01T. When in contact with magnet 8|, motor 68 will swing arm 58 to the left, and when in contact with the left magnet, will swing the rack arm 58 to the right. A second electromagnet 66 in the relay 61 swings the armature to reverse the motor 68 and move the tip of rack arm` 58 to the right. The second magnet 66 is in series with the conductors 65 from the contacts 62.

The current supply to the motor 68 from the generator I8 flows through a pair of conductors 84 which lead to normally closed contacts 85 on the oil plunger relay 18 and to a pair of normally open contacts 86 on a second oil plunger relay 81.

The relay 81 is connected through a pair of conductors 88 with a pair of normally open contacts 89 on the relay 18. A pair of normally open contacts 98 on the relay 81 are bridged across the conductors 82 to the magnet 8|. The relay 81 is set for a shorter time interval than the relay 18, for instance, the relay 81 may be set to operate in one minute and the relay 18 in three minutes.

As the re increases, the flue temperature and the CO2 content will gradually increase to bring the contact closer 51 across the contacts 62. This breaks contact at 19-88; instantly trips and opens the oil relay 18; breaks contact at 14 and allows armature 11 to start motor 41 forwardly; swings armature 83 to left and starts motor 68 forwardly. We now have a condition where both rack levers 44 and 58 are moving to the right followed by the hands 4| and 56. A point will be eventually reached when the CO2 content will begin to diminish owing to the fact that the constant increase in the air supply will provide more air than can be used by the fuel supply. This temporarily stationary value of the CO2 percentage will cause the hand 56 to stop and will break contact at 62. This causes armature 83 to reverse the CO2 indicatorA motor 68 and the armature 19 to energize the oil relay 18. The rack arm 58 now starts toward the left and if the CO2 content continues to fall for three minutes (or other interval to which the relay 18 is set) the relay 18 will act to close contacts 14 actuating relay armature 11 and reversing motor 41 to swing rack arm 44 to the left. The rack arm 44 will then cause contacts 43 to close and reverse the air control motor 2| to gradually close off the air supply. The actuation of relay 18 will also close contacts 89 and will open contacts 85. The latter opening will shut o the current supply to motor 68 so that the rack arm 58 will cease its leftwise movement. The closing at 89 will supply current to the oil relay 81. If the falling content be still uncorrected for another minute (the interval of relay 81) the relay 81 will close contacts 86. Thus again starting motor 68 so that the Contact 62 will move towards the circuit closer 51.

When contact is again made at 62 by an increase in the CO2 content, armature 83 will reverse motor 68 and open contacts 19-88 to reset relays 18, 1|, and 81; and rack levers 44 will start to the right, the air will increase, and the entire cycle will repeat.

"With the tip of rack arm 58 moving slowly to the right, contact will be broken at 51-62, allowing armature 83 to rest against contact of relay magnet 66 of relay 61. This also allows armature 19 of relay 69 to assume its normal position of contact against thereby energizing the circuit which operates the oil relay 18. If this condition maintains for the time interval to which relay 18 is adjusted, then the latter will operate to open circuit 85, and close circuits 13 and 88 at contacts 14 and 89. The opening of circuit 85 will stop the rotation of motor 68 by opening its power circuit thereby holding rack arm 58 stationary for the time being. Closing circuit 88 at contacts 89 will energize the solenoid of the second oil plunger relay 81. Closing of circuit 13 at contacts 14 will place armature 11 of relay 1| against the contact of magnet 16 and will reverse the direction of rotation of motor armature 41 sending the tip of rack arm 44 to .Y

the left to immediately reduce the amount of intake air. Should the circuit remain broken at 51-62 for the additional period of time to which the oil relay 81 is adjusted, then the latter will operate the switch assembly attached thereto closing circuit contacts 86 and 98. Closing contact 98 will attract armature 83 against the contact of magnet 8| of relay 61 setting the direction of rotation of the motor 68. Since the contacts 90 are closed at this time this will complete the power supply circuit to motor 68 thereby again starting the tip of rack arm 58 to the left to make contact again with 51. When they again meet they will reset all relays in preparation for another cycle of operation.

Normally however, the break of the circuit at 62 will be only momentary so that the delayed relay 18 will not operate.

It will be noted from the above that the optimum point of contact between 54 and 43 on the flue temperature gauge depends upon a complete combustion of the fuel then burning. It will be seen that the relation of quantity of fuel, proper air supply, flue gas temperature, and the CO2 content of the flue gases is constantly controlled so that complete combustion is had at all times. Each function affects the others in such a way to maintain a maximum CO2 content on the nue gases and a neutral flame in the fire bowl at all times.

The off scale contact 64 is provided to reverse the rack arm 58, should it accidentally reach an off scale position to the right. A second off scale contact 9| is provided on the left or zero side to be contacted by a circuit closer 92 should the rack arm reach the zero indication.

The latter condition would only occur if the re failed to ignite or became extinguished since otherwise the closer 51 would reverse the arm. The oil-scale contact 9| is connected with a suitable circuit breaker 63 which will shut off the power supply to the main driving motor I8 and actuate a signal device (not shown). Thus the entire plant would be closed down and notice given to the operator of no fire.

vMany heating plants employ an automatic switch for cutting oil. the current supply to the blowers and feed mechanism when the boiler pressure reaches a certain predetermined point. Such a switch does not take into account weather conditions etc., which might require a higher or lower boiler pressure. The present invention can be combined with a switch of this type in order to cause it to allow the boiler to build up a higher pressure in cold weather than in warm weather.

Thus it can be seen that an increasing CO2 content will cause the CO2 meter to act through the relay 10 to cause the contacts 43 in the stack thermo-gauge 40 to move to the right so that they cannot be reached by the increasing temperature hand 4|. This allows the motor 2| to progressively increase the air supply to the fire until the point is reached when the CO2 content cannot further increase and an excess of air will be entering the fire. This will cause the CO2 meter to energize the relay 10 which after a time interval to allow for a CO2 correction will swing Ythe contacts 43 in the thermogauge 49 against the temperature hand 4| to reverse the air intake control motor 2| to gradually decrease the air supply.

If this does not correct the falling content within another time interval to again return the contacts in the CO2 meter to normal the relay 81 will start the contacts 62 moving to the left in an endeavor to iind a lower CO2 point for stopping the decrease in air. If this is found, then the air supply again increases, if it is not eventually found, the entire plant will be shut down by the CO2 meter.

Thus, the system will maintain the stack temperature at the highest point consistent with the highest possible CO2 content at all times by con- -trolling the air supp'y responsive to the relation between the flue temperature and CO2 content.

Such a combination is illustrated in Fig. 4 in which a thermo-responsive device 93 is employed. This device is similar to the thermo-responsive device 23 previously described, that is, it contains the hand 25 responsive to the outside temperature and the hand 24 responsive to the burner temperature, controlled by the conductors 26 and 21 previously described. The device 93, however, contains a contact lever 94 operated from an arcuate rack 95 and worm 96. The device 93 is designed to control one of the usual mercoid switches, a typical one of which is indicated at 91.

Such a switch consists of a tilting bar 98, one extremity of which is constantly urged downwardly by a tension spring 99 and constantly urged upwardly by a plunger |00. The plunger |00 is actuated by the steam pressure in the boiler. A glass tube |02 is pivoted on the bar 98 and is provided with a quantity of mercury |03 which closes contact between the electrodes of the main electric feeds |04 to the main motor l0. The amount of pressure required to cause the plunger |00 to tilt the bar 98 so as to throw the mercury away from the electrodes is directly proportional to the amount of tension in the spring 99.

This tension is controlled by a threaded tension screw |05 actuated by a motor |06 which is caused to move forward or in reverse by means of a reversing switch |01. The reversing switch |01 has a constantly energized magnet |08 and an intermittently energized magnet |09. The intermittent magnet |09 is connected through conductors ||3 with contacts on the contact lever 94. The contacts are closed by means of a contact closer ||2 mounted on the outside temperature hand 25. The worm 96 is operated by a motor I4 which is controlled by a reversing switch H5. This switch has a constantly energized magnet ||6 and intermittently energized magnet ||1. The intermittent magnet ||1 is in the circuit of the conductors ||3 of the magnet |09 of the switch |01.

As the outside temperature falls, the hand 25 will swing to the left until it closes the contacts I. This will operate the switch |01 by energizing the magnet |09 to cause the motor |06 to increase the tension in the spring 99 so as to require a greater steam pressure in the boiler to operate the mercoid switch to cut off the current supply. At the same time it will operate the switch ||5 to cause the motor ||4 to swing the arm 94 away from the hand 25 until the contact is broken at If the outside temperature still falls the hand |25 will again make contact and repeat the process, thus the colder the weather the higher will be the steam pressure carried in the heating boiler.

While a specific form of the improvement has been described and illustrated herein, it is desired to be understood that the same may be varied, within the scope of the appended claims, without departing from the spirit of the invention.

Having thus described the invention, what is claimed and desired secured by Letters Patent l. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the flue gases and the CO2 content thereof comprising: a first thermo-gauge connected to operate in consequence of the variations in temperature of said flue gases; a lever adapted to be moved by said gauge; a rst contact carried by said lever; a second contact in the path of said first contact, said contacts being connected to control said air supply; and means for varying the position of said second contact so that the latter will be contacted at varying positions depending upon the CO2 content of said gases.

2. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the flue gases and the CO2 content thereof comprising: a first thermo-gauge connected to operate in consequence of the variations in temperature of said flue gases; a lever adapted to be moved by said gauge; a first contact carried by said lever; a second contact in the path of said first contact, said contacts being connected to control said air supply; a carbon dioxide mechanism operable by the varying CO2 content in said gases; a third contact arranged to be closed by said carbon dioxide mechanism; a motor operable by said latter contact, said motor acting to vary the position of said second contact.

3. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the flue gases and the CO2 content thereof comprising: a first thermo-gauge connected to operate in consequence of the variations in temperature of said fiue gases; a lever adapted to be moved by said gauge; a rst contact carried by said lever; a second contact ln the path of said first contact, said contacts being connected to control said air supply; a carbon dioxide mechanism operable by the varying CO2 content in said gases; a third contact arranged to be closed by said carbon dioxide mechanism; a motor operable by said latter content, said motor acting to vary the position of said second contact; and means for delaying the impuise from said carbon dioxide mechanism to said motor so that the position of said second contact will not be immediately changed.

4. Means for varying the air supply to a fuel burner comprising: a carbon dioxide gauge mechanism responsive to the CO2 content of the combustion gases; a first contact member moveable by said gauge mechanism; a second coacting contact member; a moveable support for said second contact so as to vary the point of closing said two contacts; and means for moving said support in consequence of the closing of said first and second contacts and electrical means for varying said air supply in consequence of the closing of said contacts.

5. In a fuel burner, means for maintaining the air supply to said burner at a point to produce maximum combustion of the fuel therein comprising: a thermo-responsive device operable by the variations of temperature in the flue gases of said burner; a carbon dioxide responsive device operable by the variations in the CO2 content of the combustion gases from said burner; contacts in both said responsive devices to be closed at certain positions thereof; means for automatically varying said certain positions in each of said devices in consequence of the operation of the other of said devices; and electrical means for varying said air supply in consequence of the closing of the contacts in said thermo-responsive device.

6. Means for automatically controlling combustion in a furnace comprising: a CO2 meter operable by the chemical contents of the flue gases of said furnace; a first set of contacts closed by said CO2 meter as the CO2 content increases; a thermo-responsive device actuated by variations in temperature in said furnace; a second set of contacts in said thermo-responsive device; means for moving said second set of contacts so that they will be closed at varying positions, said means for moving being controlled by said first set of contacts; and electrical means for controlling the air supply to said furnace, said latter means being controlled by said second set of contacts.

'7. Means for automatically controlling combustion in a furnace comprising: a CO2 meter operable by the chemical contents of the iiue gases of said furnace; a first set of contacts closed by said vCO2 meter as the CO2 content increases; a thermo-responsive device actuated by variations in temperature in said furnace; a second set of contacts in said thermo-responsive device; means for moving said second set of contacts so that they will be closed at varying positions, said means for moving being controlled by said first set of contacts; electrical means for controlling the air supply to said furnace, said latter means being controlled by said second set of contacts; and a dampened relay in the circuit between said first set of contacts and said means for controlling, so that the action of the latter in one direction will be delayed after said first set of contacts opens.

8. Means for automatically controlling combustion in a furnace comprising: a thermo-responsive device operable from temperature changes in said furnace; a contact closer operable by said device; movably mounted contacts positioned to be closed by said closer; a motor for varying the position of said contacts; a CO2 meter operable from variations in the CO2 content of the flue gases of said furnace; other contacts adapted to be closed by said CO2 meter; and a relay in circuit with said latter contacts and said motor and operating the latter in consequence of operation of said CO2 meter; and electrical means operable by said first set of contacts for controlling the air supply to said furnace.

9. Means for automatically controlling combustion in a furnace comprising: means for feeding fuel to said furnace; a first movable contact, the moving ef which is in consequence of the variations of temperature in said furnace; a second contact arranged to close the circuit with said first contact; means for moving said second contact in consequence of variations in temperature outside said furnace; a reversing relay operable by the opening and closing of said contacts; and electrical means for controlling the means for feeding fuel in consequence of the action of said relay.

l0. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the iiue gases of said burner and the CO2 content thereof, comprising: a first electrical Contact; means for moving said first contact in a fixed path in consequence of variations in temperature of said fiue gases; a second coacting electrical'contact; means for moving said second Contact in the same fixed path in consequence of variations in the CO2 content of said flue gases; and an electrical circuit for controlling the air supply to said burner, said circuit including and being controlled by said two contacts.

1l. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the flue gases of said burner and the CO2 content thereof, comprising: a thermo-respo-nsive device having a pivoted lever swinging in consequence of the variations in temperature of said flue gases; a first contact carried by said lever; a second movably-mounted contact in the path of said first contact; means for varying the contacting position of said second contact in consequence of variations in the CO2 content of said flue gases; electrical means for controlling the air supply to said burner; and an electric circuit including said two contacts and said electrical means so that said contacts will close said circuit at varying positions of said second contact.

l2. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the fiue gases of said burner and the CO2 content thereof, comprising: a first contact; means for moving said first contact in a fixed path in consequence of variations in the temperature of said fiue gases; a second coacting contact; means for movably supporting said second contact in the path of said first contact; a CO2 mechanism; a third contact positioned to be closed by said CO2 mechanism; a first electric circuit including said third contact; means for moving said secon-d contact in consequence of the closing of said first circuit; and a second circuit for controlling the air supply to said burner, said second circuit including said rst and second contacts.

13. Means for controlling the air supply to a burner in consequence of the relation between the temperature of the flue gases of said burner and the CO2 content thereof, comprising: a first contact; means for moving said first contact in a xed path in consequence of variations in the temperature of said flue gases; a second coacting contact; means for movably supporting said second contact in the path of said first contact; a CO2 mechanism; a third contact positioned to be closed by said CO2 mechanism; a rst electric circuit including said third contact; meansfor moving said second contact in consequence of the closing of said first circuit; a second circuit for controlling the air supply to said burner, said second circuit including said first and second contacts; and means for delaying the closing of said rst circuit for a predetermined interval.

14. Means for varying the air supply to a fuel burner comprising; a CO2 mechanism responsive to the CO2 content of the combustion gases of said burner; a first contact movable by said CO2 mechanism; a second movable contact in the path of said first contact; a movable support for said second contact; a third contact, said movable support being positioned between said rst and third contacts; a fourth contact carried by said movable support; means for moving said support in one direction in consequence of the closing of said rst and second contacts and in the other direction in consequence of the closing of said third and fourth contacts; and electrical means for varying said air supply in consequence of the closing of said first and second contacts.

HENRY J. KEELEY.

CII 

